如图所示，

将若干个点摆成三角形图案，每条边（包括两个端点）有n（n是正整数且n＞1）个点，相应的图案中总的点数记为a_n ，则 $\frac{9}{a_2{a}_3}$ + $\frac{9}{a_3{a}_4}$ +…+ $\frac{9}{a_{2017}{a}_{2018}}$ =（   ）

    As a foreigner, it's hard for me to tell what Chinese people are like. But my1in Beijing said something.

    A couple of weeks ago, I went to buy four big suitcases(行李箱) for travel.2I was going down the street, it suddenly rained, heavily. A stranger called me into his little shop. He 3 me a cup of tea and a chair. When the rain got 4, I thanked him and rushed to a5nearby to buy my suitcases.

    If you've ever tried to push four big suitcases by yourself, you may understand my6. I looked silly, for the suitcases were dancing wildly across the floor. Then I got a7on the shoulder. It was the seller. He signed that I should wait. A few minutes later, he8in a car, and put the suitcases inside. Then we went driving9along the road to my home. I offered him some money, but he10. In broken English he said, “Feel good…help you.”

    Now, you can see Chinese people are always ready to help you.